Ram A. Hashmonay

Open-Path Tunable Diode Laser Absorption Spectroscopy for Acquisition of Fugitive Emission Flux Data

Abstract Air pollutant emission from unconfined sources is an increasingly important environmental issue. The U.S. Environmental Protection Agency (EPA) has developed a ground-based optical remote-sensing method that enables direct measurement of fugitive emission flux from large area sources. Open-path Fourier transform infrared spectroscopy (OP–FTIR) has been the primary technique for acquisition of pollutant concentration data used in this emission measurement method. For a number of environmentally important compounds, such as ammonia and methane, open-path tunable diode laser absorption spectroscopy (OP–TDLAS) is shown to be a viable alternative to Fourier transform spectroscopy for pollutant concentration measurements. Near-IR diode laser spectroscopy systems offer significant operational and cost advantages over Fourier transform instruments enabling more efficient implementation of the measurement strategy. This article reviews the EPA’s fugitive emission measurement method and describes its multipath tunable diode laser instrument. Validation testing of the system is discussed. OP-TDLAS versus OPFTIR correlation testing results for ammonia (R 2 = 0.980) and methane (R 2 = 0.991) are reported. Two example applications of tunable diode laser-based fugitive emission measurements are presented.

Probing emissions of military cargo aircraft: description of a joint field measurement Strategic Environmental Research and Development Program.

Abstract To develop effective air quality control strategies for military air bases, there is a need to accurately quantify these emissions. In support of the Strategic Environmental Research and Development Program project, the particulate matter (PM) and gaseous emissions from two T56 engines on a parked C-130 aircraft were characterized at the Kentucky Air National Guard base in Louisville, KY. Conventional and research-grade instrumentation and methodology were used in the field campaign during the first week of October 2005. Particulate emissions were sampled at the engine exit plane and at 15 m downstream. In addition, remote sensing of the gaseous species was performed via spectroscopic techniques at 5 and 15 m downstream of the engine exit. It was found that PM mass and number concentrations measured at 15-m downstream locations, after dilution-correction generally agreed well with those measured at the engine exhaust plane; however, higher variations were observed in the far-field after natural dilution of the downstream measurements was accounted for. Using carbon dioxide-normalized data we demonstrated that gas species measurements by extractive and remote sensing techniques agreed reasonably well.

Measurement of greenhouse gas emissions from agricultural sites using open-path optical remote sensing method.

Improved characterization of distributed emission sources of greenhouse gases such as methane from concentrated animal feeding operations require more accurate methods. One promising method is recently used by the USEPA. It employs a vertical radial plume mapping (VRPM) algorithm using optical remote sensing techniques. We evaluated this method to estimate emission rates from simulated distributed methane sources. A scanning open-path tunable diode laser was used to collect path-integrated concentrations (PICs) along different optical paths on a vertical plane downwind of controlled methane releases. Each cycle consists of 3 ground-level PICs and 2 above ground PICs. Three- to 10-cycle moving averages were used to reconstruct mass equivalent concentration plum maps on the vertical plane. The VRPM algorithm estimated emission rates of methane along with meteorological and PIC data collected concomitantly under different atmospheric stability conditions. The derived emission rates compared well with actual released rates irrespective of atmospheric stability conditions. The maximum error was 22 percent when 3-cycle moving average PICs were used; however, it decreased to 11% when 10-cycle moving average PICs were used. Our validation results suggest that this new VRPM method may be used for improved estimations of greenhouse gas emission from a variety of agricultural sources.

Line profile reconstruction: validation and comparison of reconstruction methods

Abstract Currently, open path Fourier transform infrared (OP-FTIR) spectrometers have been applied in some fenceline monitoring, but their use has been limited because path-integrated concentration measurements typically only provide an estimate of the average concentration. We present a series of experiments that further explore the use of path-integrated measurements to reconstruct various pollutant distributions along a linear path. Our experiments were conducted in a ventilation chamber using an OP-FTIR instrument to monitor a tracer-gas release over a fenceline configuration. These experiments validate a line profile method (1-D reconstruction). Additionally, we expand current reconstruction techniques by applying the Bootstrap to our measurements. We compared our reconstruction results to our point samplers using the concordance correlation factor (CCF). Of the four different release types, three were successfully reconstructed with CCFs greater than 0.9. The difficult reconstruction involved a narrow release where the pollutant was limited to one segment of the segmented beampath. In general, of the three reconstruction methods employed, the average of the bootstrapped reconstructions was found to have the highest CCFs when compared to the point samplers. Furthermore, the bootstrap method was the most flexible and allowed a determination of the uncertainty surrounding our reconstructions.

Applying Open-Path FTIR with a Bi-Beam Strategy to Evaluate Personal Exposure in Indoor Environments: Experimental Results of a Validation Study

This study evaluated the performance and feasibility of using open-path Fourier transform infrared (OP-FTIR) with a bi-beam strategy to assess personal exposures in workplaces. The bi-beam strategy combines a long beam and a short beam measurement to calculate the average concentration level of the segmented region. A series of experiments was conducted with six human subjects at two workstations inside a chamber. A bi-beam geometry was set up for each workstation. Each subject repeatedly performed two tasks (9 min/task), which were designed to simulate a painting and an assembly task. For each task a tracer gas (N(2)O) was released from a point source near the subject. During each task, while the OP-FTIR collected the N(2)O spectrum, bag samples were collected simultaneously at nose and lapel height. Statistical data analysis applied a general linear model with the bag samples as the dependent variable. Results show that the locations, tasks, and subjects are not significant factors when using OP-FTIR measurements with the bi-beam strategy to estimate personal exposure at the nose height. The model used in this study fits the data reasonably well (R(2)=0.87), and when it is compared with a second set of experimental data, the bias is 0.7 ppm (3%) and the precision is 5.5 ppm. This study demonstrates that the bi-beam sampling strategy may offer a new approach for applying OP-FTIR to industrial hygiene monitoring.

An Advanced Test Method forMeasuring Fugitive Dust Emissions Using a Hybrid System of Optical Remote Sensing and PointMonitor Techniques

A new test method for measuring fugitive dust emissions has been developed. This method includes one open path laser transmissometer (OPLT) extended to a path of several undred meters to measure ground-level extinction coefficients across an entire plume combined with one tower with at least two vertically distributed and time-resolved dust monitors (DM) (in the middle of the OP-LT path) to measure vertical gradients of PM10 and PM2.5 concentration. At least two wind monitors are mounted on the tower at the same elevation as the DM instruments to measure wind speed and wind direction for input into the PM flux calculations. The extinction data from the OP-LT (from a specific dust source) are calibrated to the PM10 concentration data from calibrated DM instruments. We found that such calibration is mainly a function of dust type and its typical airborne particle size distribution. The performance of this method is demonstrated through comparison to a more traditional upwind-downwind method that deploys three towers with five DM instruments on each tower to define the flux plane with multiple measurements. It is shown that the new hybrid method (one tower with two or three DM instruments and OP-LT) provides comparable flux calculation to the traditional method.

Theoretical Evaluation of a Method for Locating Gaseous Emission Hot Spots

Abstract This paper describes and theoretically evaluates a recently developed method that provides a unique methodology for mapping gaseous emissions from non-point pollutant sources. The horizontal radial plume mapping (HRPM) methodology uses an open-path, path-integrated optical remote sensing (PI-ORS) system in a horizontal plane to directly identify emission hot spots. The radial plume mapping methodology has been well developed, evaluated, and demonstrated. In this paper, the theoretical basis of the HRPM method is explained in the context of the method’s reliability and robustness to reconstruct spatially resolved plume maps. Calculation of the condition number of the inversion’s kernel matrix showed that this method has minimal error magnification (EM) when the beam geometry is optimized. Minimizing the condition number provides a tool for such optimization of the beam geometry because it indicates minimized EM. Using methane concentration data collected from a landfill with a tunable diode laser absorption spectroscopy (TDLAS) system, it is demonstrated that EM is minimal because the averaged plume map of many reconstructed plume maps is very similar to a plume map generated by the averaged concentration data. It is also shown in the analysis of this dataset that the reconstructions of plume maps are unique for the optimized HRPM beam geometry and independent of the actual algorithm applied.

A Novel Method to Quantify Fugitive Dust Emissions Using Optical Remote Sensing

Abstract : This paper describes a new method for retrieving path-averaged mass concentrations from multi-spectral light extinction measured by optical remote sensing (ORS) instruments. The light extinction measurements as a function of wavelength were used in conjunction with an iterative inverse-Mie algorithm to retrieve path-averaged particulate matter (PM) mass distribution. Conventional mass concentration measurements in a controlled release experiment were used to calibrate the ORS method. A backscattering micro pulse lidar (MPL) was used to obtain the horizontal extent of the plume along MPLs line of sight. This method was used to measure concentrations and mass emission rates of PM with diameters smaller or equal to 10 microns (PM(sub 10)) and PM with diameters smaller or equal to 2.5 microns (PM(sub 2.50) that were caused by dust from an artillery back blast event at a location in a desert region of the southwestern United States of America.

Characterization of Fugitive Emissions of Greenhouse Gases from a Wastewater Treatment Plant Using the Radial Plume Mapping Technique

An existing anaerobic wastewater treatment plant (WWTP) near Bucaramanga, Colombia is being upgraded to include nitrification/denitrification and improvements in capture and recovery of methane. The existing plant utilizes upflow anaerobic sludge blanket (UASB) reactors followed by facultative lagoons. For this project, the UASB reactors will be retrofit to maximize the collection of biogas, and the lagoons will be converted into an aerobic/anoxic activated sludge (aerated oxidation tank) process for biological nitrogen removal. It is anticipated that the upgrade will result in a reduction in odors associated with plant operation, and a net reduction in greenhouse gas emissions via the recovery of methane and the reduction in nitrous oxide emissions from the plant and the receiving river. This will result in carbon credits under the Kyoto Protocol’s clean development mechanism (CDM) which would be purchased by carbon finance trust funds at the World Bank. In order to document the emissions reductions, an accurate and cost-effective monitoring of the emissions before and after the upgrades is crucial to the success of the project.

Extractive sampling and optical remote sensing of F100 aircraft engine emissions.

Abstract The Strategic Environmental Research and Development Program (SERDP) has initiated several programs to develop and evaluate techniques to characterize emissions from military aircraft to meet increasingly stringent regulatory requirements. This paper describes the results of a recent field study using extractive and optical remote sensing (ORS) techniques to measure emissions from six F-15 fighter aircraft. Testing was performed between November 14 and 16, 2006 on the trim-pad facility at Tyndall Air Force Base in Panama City, FL. Measurements were made on eight different F100 engines, and the engines were tested on-wing of in-use aircraft. A total of 39 test runs were performed at engine power levels that ranged from idle to military power. The approach adopted for these tests involved extractive sampling with collocated ORS measurements at a distance of approximately 20–25 nozzle diameters downstream of the engine exit plane. The emission indices calculated for carbon dioxide, carbon monoxide, nitric oxide, and several volatile organic compounds showed very good agreement when comparing the extractive and ORS sampling methods.